This application is based on and incorporates herein by reference Japanese Patent Application No. 2000-320835 filed on Oct. 20, 2000.
1. Field of the Invention
The present invention relates to a vapor fuel processing system for dissolving vapor fuel, which is generated in a fuel tank and is absorbed by a canister, into liquid fuel received in the fuel tank.
2. Description of Related Art
In a previously proposed vapor fuel processing system, vapor fuel generated in the fuel tank is absorbed by activated carbons received within a canister and is discharged into an intake air pipeline of an intake air system that supplies intake air to an engine, so that the vapor fuel discharged into the intake air pipeline is combusted in the engine. However, in this system, a deviation in an air-fuel ratio occurs due to the vapor fuel discharged into the intake air pipeline. This may result in an increase in the amount of noxious components contained in exhaust gas of the vehicle. This is not favorable for satisfying various emission standards, such as the SULEV standard. Thus, it is desirable to reduce the amount of the vapor fuel discharged into the intake air pipeline.
Furthermore, there is a strong demand for improving fuel consumption of vehicles. In an engine that can achieve improved fuel consumption, a negative pressure of intake air is reduced due to a reduction in a pumping loss and an increase in fuel combustion in a lean fuel range. In the engine that has the reduced negative pressure of the intake air, the amount of the vapor fuel, which is absorbed by the canister and is then removed from the canister into the intake air pipeline through use of the negative pressure of the intake air, is reduced.
The system that discharges the vapor fuel into the intake air system can be modified as follows. That is, the vapor fuel absorbed by the canister from the fuel tank may be suctioned into and pressurized within a pressurizing pump. Then, the pressurized vapor fuel may be discharged into a pressure tank maintained at a high pressure to liquefy the vapor fuel. Thereafter, the liquefied fuel under the high pressure may be discharged into a fuel supply line.
However, when the pump suctions the vapor fuel from the canister, the air is also suctioned along with the vapor fuel, so that the air is also dissolved into the pressurized liquefied fuel. Thus, the fuel that contains the dissolved air is supplied to the engine. When the fuel pressure decreases, for example, right after engine stop, the air dissolved in the fuel is depressurized and becomes air bubbles, making it difficult to restart the engine.
Thus, it is an objective of the present invention to provide a vapor fuel processing system that can process vapor fuel regardless of a degree of a negative pressure of intake air and can restrain a deviation in an air-fuel ratio.
To achieve the objective of the present invention, there is provided a vapor fuel processing system including a fuel tank, a pressure tank, a pressure control valve, a canister and a pressurizing pump. The fuel tank receives liquid fuel. The pressure tank is arranged within the fuel tank and receives liquid fuel supplied from the fuel tank. The pressure control valve is arranged between the fuel tank and the pressure tank. The pressure control valve is opened to communicate between an inside of the pressure tank and an inside of the fuel tank when a pressure within the pressure tank becomes equal to or greater than a predetermined pressure. The canister absorbs vapor fuel contained in the fuel tank. The pressurizing pump is arranged between the canister and the pressure tank. The pressurizing pump suctions the vapor fuel from the canister and discharges the vapor fuel into the liquid fuel in the pressure tank upon pressurizing the vapor fuel in the pressurizing pump to dissolve the vapor fuel into the liquid fuel in the pressure tank.